The present invention is directed to a display device which includes a light valve that is operated in a time division multiplex (TDM) process such as a liquid crystal display and a plate-shaped body containing a material having an index of refraction greater than 1 and fluorescent particles to form a fluorescent plate.
A display utilizing a light valve, which operates in a time division multiplex (TDM) method or process and has a fluorescent body or plate, is disclosed in German Utility Pat. No. 7724216, whose disclosure is incorporated in United States Patent Application Ser. No. 929,496 filed July 31, 1978 which issued on May 27, 1980 as U.S. Pat. No. 4,204,399.
In electro-optical displays in which the transition time between the various optical states are relatively long, for example a liquid crystal display based on a DAP effect or the Schadt-Helfrich effect, the multiplex ratio, which can be achieved, is primarily dependent upon the steepness of the gradient of the contrast-voltage curve in the transition range. For example, see the article in Journal of Applied Physics, Vol. 48, No. 4, April 1977, pp. 1426-1431. This gradient can reach values, which facilitate more than 100 multiplex steps; however, since the contrast-voltage characteristic is also sensitive to the direction of the oncoming radiation, this large number of steps can only be achieved when sharply focused light is used.
The previous methods of producing light cones required in highly multiplexable displays was to employ a sharply directed illumination or a suitable projection. Since these require complicated construction, consumed additional power, and in particular, convert a passive display into a quasi-active display having a contrast which is dependent upon the environment, these measures have proven to be particularly unsatisfactory.
If the light valve is combined with a fluorescent plate, which acts as a light trap and is provided with light exit windows, the representation contrast and the image brightness of the light valve can be considerably increased in a purely passive fashion and thus without any consumption of energy. A "fluorescent activated display" (FLAD) of this type is known and is disclosed, for example, in German OS No. 25 54 226, whose disclosure is incorporated in United States Patent Application Ser. No. 747,035 filed on Dec. 2, 1976, which issued on Mar. 6, 1979 as U.S. Pat. No. 4,142,781, and is also disclosed and discussed in an article in Electronics, Dec. 8, 1977, pp. 113-116. In an FLAD, the spatial angle range of the light emitted from the fluorescent plate can be constricted through specially shaped outlet or exit windows. Examples of this are disclosed in the above mentioned United States Patent Application Ser. No. 747,035. However, a disadvantage of these window designs is that the light component, which is not output coupled from the window remains in the fluorescent plate and thus, the brightness amplification factor is reduced by the limitation of the light outlet cone.